Aircraft landing at airports during marginal Visual Meteorological Conditions (VMC) or in cases of reduced cues such as night flight are aided by an Instrument Landing System (ILS). The ILS is a radio beam that originates on the ground at an ILS equipped airport and generates a glide slope that an aircraft can safely follow during an instrument approach to the runway. The ILS radio beam is detected by equipment onboard the aircraft and provides lateral, along-course, and vertical guidance to aircraft attempting to land at an ILS equipped airport. However, not all airport runways have an ILS generated radio glideslope.
Airports may substitute or also provide airport lighting aids as described in the Aeronautical Information Manual (AIM) for Basic Flight Information and ATC Procedures at Chapter 2: AERONAUTICAL LIGHTING AND OTHER AIRPORT VISUAL AIDS as published by the FAA (Federal Aviation Administration (U.S.)), which is incorporated herein by reference in its entirety. The airport lighting aids may provide vertical visual approach slope guidance to the runway, which is especially useful during marginal Visual Meteorological Conditions (VMC) or in cases of reduced cues. For example, various known Approach Light Systems (ALS) provide the basic means to transition from instrument flight to visual flight for landing. Operational requirements dictate the sophistication and configuration of the ALS for a particular runway. ALS are a directional pattern of high intensity signal lights starting at a landing threshold of the runway and extending a prescribed distance into the approach area. The signal lights shine upwardly toward the aircraft along the approach slope or glide path that guide the pilot visually during approach and landing. Some ALS include sequenced flashing lights which appear to the pilot as a ball of light traveling towards the runway at high speed. A number of precision and nonprecision configurations of ALS are known and illustrated in the AIM at Chapter 2. These known ALS and equivalents thereof are considered within the scope of the simulated airport lighting aid invention.
Another known airport lighting aid is the Precision Approach Path Indicator (PAPI) system, as described in the FAA's AERONAUTICAL LIGHTING AND OTHER AIRPORT VISUAL AIDS and in FAA Advisory Circular AC 150/5345-28D, dated May 23, 1985, incorporating Change 1, Subject: Precision Approach Path Indicator (PAPI) systems, which is incorporated in its entirety herein by reference. The PAPI uses a single row of either two or four light units. These systems have an effective visual range of about 5 miles during the day and up to 20 miles at night. The row of light units is normally installed on the left side of the runway as shown in FIGS. 1 and 2, in which the glide path indications are as depicted.
According to the PAPI system, either two or four identical light units are placed on one side of the runway in a line perpendicular to the runway centerline to define the visual glide path angle. The light units each have a white segment in an upper part of the beam and red segment in a lower part of the beam separated by a pink transition zone. In the two-light Type L-881 system shown in FIG. 1, the lights are positioned and aimed to produce a signal presentation wherein a pilot on or close to the established approach path (center) sees the light unit nearest the runway as red (shown as a darkened circle) and the other light unit as white (shown as white in a black circle). When above the approach path (right) the pilot sees both light units as white; and when below the approach path (left) the pilot sees both light units as red.
According to the four-light Type L-880 system PAPI system shown in FIG. 2, the signal presentation is such that a pilot on or close to the established approach path (center) sees the two light units nearest the runway as red and the two light units farthest from the runway as white. When above the approach path (center right) the pilot sees the light unit nearest the runway as red and the three light units farthest from the runway as white; and when further above the approach path (far right) the pilot sees all the light units as white. When below the approach path (center left) the pilot sees the three light units nearest the runway as red and the light unit farthest from the runway as white; and when further below the approach path (far left) the pilot sees all light units as red.
The visual glide path angle provided by the PAPI is the center of the center of the on-course zone, and is normally 3 degrees when measured from the horizontal, but may vary if jet aircraft are supported by the airport, if obstacles to flight are located at the airport, or if elevated terrain affects the approach to the airport. Other considerations in siting the PAPI indicator lights include whether the terrain drops off rapidly near the approach threshold, and whether severe turbulence is experienced on approach. On short runways, the PAPI indicator lights are located as near the threshold as possible to provide the maximum amount of runway for braking after landing. Thus, the PAPI indicator lights are positioned and aimed to produce a minimum Threshold Crossing Height (TCH), which is the height of the lowest on-course signal at a point directly above the intersection of the runway centerline and the threshold, and clearance over obstacles in the approach area.
FIG. 3 illustrates a known tri-color airport lighting aid system. Tri-color visual approach slope indicators normally consist of a single light unit projecting a three-color visual approach path into the final approach area of the runway. The below glide path indication is red, the above glide path indication is amber, and the on glide path indication is green. Tri-color visual approach slope indicators have a useful range of approximately one-half to one mile during the day and up to five miles at night depending upon the visibility conditions.
FIG. 4 illustrates a known pulsating airport lighting aid system in which the visual approach slope indicators normally consist of a single light unit projecting a two-color visual approach path into the final approach area of the runway. The on glide path indication is a steady white light. The slightly below glide path indication is a steady red light. If the aircraft descends further below the glide path, the red light starts to pulsate. The above glide path indication is a pulsating white light. The pulsating rate increases as the aircraft deviates further above or below the desired glide path. The useful range of the pulsating light system is about four miles during the day and up to ten miles at night.
FIG. 5 illustrates a Visual Approach Slope Indicator (VASI) system, as described in the FAA's AERONAUTICAL LIGHTING AND OTHER AIRPORT VISUAL AIDS, and in each of FAA Advisory Circulars AC 150/5340-25 dated Sep. 24, 1976, and AC 150/5345-28C dated Mar. 23, 1976, both incorporated in their entirety herein by reference. The VASI is another known airport lighting aid system that provides a visual glide path angle by directing a beam of light at approaching aircraft to indicate to the pilot whether the aircraft is within the appropriate glide path for approaching the intended runway. VASI lighting aid systems are visible from 3–5 miles during the day and up to 20 miles or more at night, and are arranged to provide visual descent guidance information during the approach after the aircraft is visually aligned with the runway. Lateral course guidance is provided independently by the runway or runway lights. As described in the FAA's AERONAUTICAL LIGHTING AND OTHER AIRPORT VISUAL AIDS, VASI installations are typically either 2, 4, 6 12, or 16, light units arranged in bars referred to as near, middle, and far bars. Most VASI installations are 2 bars, near and far, and may include 2, 4, or 12 light units, as described in U.S. Pat. No. 3,939,571, METHOD AND APPARATUS FOR AIMING AIRCRAFT VISUAL APPROACH SLOPE INDICATOR, which is incorporated in its entirety herein by reference. Two-bar VASI installations provide one visual glide path which is normally set at 3 degrees. Some VASI are three bars spaced intermittently along one or both sides of the runway, near, middle, and far, such as to provide an additional visual glide path to accommodate high cockpit aircraft. Three-bar VASI installations provide two visual glide paths. The lower glide path is provided by the near and middle bars and is normally set at 3 degrees while the upper glide path, provided by the middle and far bars, is normally ¼ degree higher. This higher glide path is intended for use only by high cockpit aircraft to provide a sufficient threshold crossing height or TCH. Although normal glide path angles are 3 degrees, angles at some locations may be steeper to give proper obstacle clearance. VASI installations having 2, 4, or 6 light units are located on one side of the runway, usually the left. Where the installation includes 12 or 16 light units, the units are usually located on both sides of the runway.
The basic principle of the VASI is that of color differentiation between red and white. Each light unit aims a narrow split beam of light at approaching aircraft. The lights each have a white segment in the upper part of the beam and red segment in the lower part of the beam with the transition zone being pink. The light units are arranged so that the pilot using the VASI during an approach sees the combination of lights shown in FIG. 5 for a 2-bar VASI (4 light units) system. The farthest light unit of a two unit system, for example, is aligned and positioned so that the bottom of the red or lower segment (shown as a darkened circle) is parallel to the glide path and forms the upper limit of an ideal glide path for the runway. In such a system, the light unit closest to approaching aircraft is aligned and positioned so that the top of the white or upper segment (shown as white in a black circle) is aimed into the glide path, and the bottom of the white segment is approximately parallel to the glide path and forms the lower limit of the ideal glide path. When an aircraft is on the proper glide path (center) the closest unit appears white to the pilot and the farthest appears red. If the approach is too high (right) both units are seen as white, and a low approach (left) is indicated by both units appearing red.
The PAPI and VASI airport lighting aid systems are controlled from the ground. However, as described in FAA Advisory Circular AC 150/5340-27A, dated Mar. 4, 1986, Subject: Air-to-Ground Control of Airport Lighting Systems, which is incorporated in its entirety herein by reference, radio control of airport lighting aids is available at selected airports to provide airborne control of lights by keying the aircraft's microphone. Control of lighting systems is often available at locations without specified hours for lighting and where there is no control tower or Flight Service Station (FSS) or when the tower or FSS is closed (locations with a part-time tower or FSS) or specified hours.
While airport lighting aids such as PAPI or VASI or another lighting aid are located at most airports, not all airports provide either an ILS radio glideslope or a visual glide path angle; approach safety is thereby degraded during marginal Visual Meteorological Conditions (VMC) or in cases of reduced cues such as night flight.
U.S. Pat. No. 4,210,930, APPROACH SYSTEM WITH SIMULATED DISPLAY OF RUNWAY LIGHTS AND GLIDE SLOPE INDICATOR, issued to Richard D. Henry on Jul. 1, 1980, attempts to provide simulated runway lights and Visual Approach Slope Indicator (VASI) for the pilot using an airborne image camera, its respective image scan plate and image Cathode Ray Tube (CRT) to form a display that portrays what the pilot would see, were it not for limited visibility conditions. The on-board CRT continuously enacts and displays, according to position of the aircraft, what would otherwise be visible to the pilot as the runway lights of an illuminated runway, were it not for obscured vision. This is obtainable by RF microwave signals from a plurality of from ground-based emitters at spaced locations along the length of a runway and at approximately the same locations as the runway lights thereon and reflectors which reflect the RF wave energy to the opposite ends of the runway. The RF emitters and reflectors substitute RF energy for visible spectrum light. The RF energy from the ground-based portion of the system is received and processed by instruments in the aircraft to create a display on the CRT.
While the ground-based RF system of providing simulated runway lights and Visual Approach Slope Indicator (VASI) may be useful in limited visibility conditions, the system requires that airports be equipped with additional equipment and energy sources along the runway with the aircraft using receptor equipment to detect the energy. Such a system fails to provide a simulated glideslope or visual glide path angle if not all airports are equipped with the RF emitters and reflectors.